Steam the fiddleheads over boiling water for about five minutes, or until they are crispy-tender. Drain them and place them immediately into a bowl of ice water to stop the cooking. Let them sit for only about 30 seconds to a minute, then transfer them to paper towels to drain.

Whisk the yogurt, mayonnaise, lemon juice, mustard, horseradish, ramps, and salt and pepper together in a bowl.- until smooth.